Axial flow turbine structure

ABSTRACT

In the manufacturing of stator vanes for the first stage of a multi-stage axial flow gas turbine, casting difficulty and casting cost are reduced by making a separate casting for each vane instead of making segmental groups of vanes which are costly due to a high casting rejection rate. The vanes are supported by grooved holding blocks attached to the blade ring of the turbine, and they are readily assembled or removed. An improved cooling system is provided for the vanes which are of a hollow construction.

United States Patent Rahaim et a1.

[ 1 Sept. 5, 1972 AXIAL FLOW TURBINE STRUCTURE Inventors: Thomas J. Rahaim, Claymont, DeL; George M. Mierley, Sr., Lake Worth, Fla.

Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

Filed: Jan. 11, 1971 Appl. No.: 105,551

US. (:1. ..415/115, 415/217, 415/1 16 1m. 01. "mm 25/12, FOld 9/00 Field ofSearch AIS/115,116,117,131,134, 415/138, 216, 217,218

References Cited UNITED STATES PATENTS 3,362,681 1/1968 Smuland ..415/134 Primary Examiner-Henry F. Raduazo Attorney-A. T. Stratton, F. P.-Ly1e and F. Cristiano,

[ ABSTRACT In the manufacturing of stator vanes for the first stage of a multi-stage axial flow gas turbine, casting difiiculty and casting cost are reduced by making a separate casting for each vane instead of making segmental groups of vanes which are costly due to a high casting rejection rate. The vanes are supported by grooved holding blocks attached to the blade ring of the turbine, and they are readily assembled or removed. An improved cooling system is provided for the vanes which are of a hollow construction.

7Claims,7DrawingFigures 1 AXIAL FLOW TURBINE STRUCTURE BACKGROUND OF THE INVENTION This invention relates, generally, to axial flow turbine structures and, more particularly, to stator vane structures for the first stage of a multi-stage axial flow gas turbine.

Heretofore, the stator vanes for axial flow gas turbines have been cast in segmental groups of, for example, four vanes in each group. This has been difficult and costly due to a high casting rejection rate. Also, the segments have been installed by inserting them in grooves in the blade ring extending transversely of the turbine axis. This made removal and replacement of a segmental group difficult and time consuming.

BRIEF SUMMARY OF THE INVENTION In accordance with this invention, each stator vane structure, for the first stage of a multi-stage axial flow gas turbine is made a separate casting. The vane structures are supported by axially grooved holding blocks attached to the blade ring of the turbine. Axially spaced holding lugs on each vane structure slide axially of the turbine in grooves in two adjacent blocks. Thus, each vane structure can be removed and replaced separately from the other vane structures. The vanes are of a hollow construction, and cooling air is admitted into each vane through an opening in each holding block into a separate air chamber for each vane, so that failure of any one vane will not rob its neighbors of their air supply.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the nature of the invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a view, partly in elevation and partly in axial section, of a portion of a gas turbine incorporating the invention;

FIG. 2 is a view, in plan, of one of the holding blocks utilized in the structure shown in FIG. 1;

FIG. 3 is a projected side elevation, of a portion of DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, particularly to FIG. 1, the structure shown therein comprises a portion of the first stage of an axial flow gas turbine 10 which includes an annular array of separate first stage stator vane structures 12 (only one shown) and an annular row of first stage rotor blades 14 (only one shown) disposed immediately downstream from the stationary vanes 12. The rotor blades 14 are suitably attached to the periphery of a rotor disc 15, only a portion of which is shown, secured to ,a shaft (not shown) rotatably mounted in the turbine casing in a manner well known in the art. The turbine 10 may include additional expansion stages comprising stationary vanes and rotary blades disposed downstream from the blades 14, thereby providing a multi-stage turbine.

A hot motive gas is supplied to the turbine from suitable combustion chambers (not shown). The hot motive gas flows from the combustion chambers through the stationary vanes and the rotating blades, thereby driving the turbine shaft by energy extracted from the hot motive fluid, in a manner well known in the art.

As shown in FIG. 1, the stator vane structures 12 are mounted in a stator blade ring 16 which may be of a fabricated construction comprising a plurality of annular sections 18 of different diameters welded together. The blade ring 16 is disposed inside a turbine casing (not shown) which is generally circular in cross section. A cover 20 may be attached to the blade ring 16 in a suitable manner. In accordance with the usual practice, arcuate ring segments 22 are mounted in a T-shaped groove 24 in the inner periphery of a section 18 of the blade ring 16 around the rotor blades 14 to reduce leakage of the motive fluid past the rotor blades durin operation of the turbine.

Heretofore, the stator vanes have been cast in segmental groups of vanes with a certain number of vanes, for example four, secured between an arcuate outer shroud segment and an inner arcuate shroud segment. The outer shroud segments have been mounted in a groove in the blade ring in a manner similar to the ring segments 22. The prior method of casting the vanes in groups has been difficult and costly due to a high casting rejection rate.

In accordance with the present invention, each vane structure 12 for the first stage of the turbine is cast separately with a vane portion 26 secured between an outer shroud portion 28 and an inner shroud portion 30, thereby simplifying the casting procedure. The outer shroud portions 28 are supported in holding blocks 32 attached to the blade ring 16 by means of screws 34 extending through the blade ring and threaded into holes 36 in each block 32. Additional positioning means for each holding block may be provided by a pin 38 inserted through a flange 40 on the blade ring 16 into one end of each block 32.

As shown more clearly in FIGS. 2 to 6, each holding block 32 is generally parallelogram shaped with an inwardly extending projection 42 on one side of the block. The projection 42 has axially extending grooves 44 and 46 therein for receiving holding lugs 48 on the outer shroud 28 of the vane structure 12, see FIG. 7. Each block has a slight curvature corresponding to the curvature of the blade ring. The blocks 32 may be made by cutting a ring having a generally rectangular cross section with an outside diameter substantially equal to the inside diameter of the first section 18 of the blade ring 16 into a predetermined number of pieces, for example 40. Thus, each block, extends through an arc of 9. The grooves 44 and 46 are machined in each block. Likewise, the holes 36 are drilled and tapped in each block. An opening 50 is drilled through each block for admitting cooling air into each vane 26 which is of a hollow construction. A

hole 52 is drilled in one end of each block for receiving the pin 38. As previously explained, each block 32 is attached to the blade ring 16 by means of two screws 34 threaded into the holes 36.

An advantage of the present structure is thatby providing the vane retaining grooves in separate high strength blocks, the blade ring proper may be made of a less expensive material. Also, since the holding blocks are separate from the blade ring, they may be machined on relatively small machine tools which have a lower cost rate than larger tools required for machining the relatively large blade ring.

As shown in FIG. 7, each vane structure 12 comprises the vane portion 26,which is of a hollow construction, secured between the outer shroud portion 28.

and the inner shroud portion 30. Two transversely spaced rows of holding lugs 48 are formed integrally with the outer shroud portion 28. In order to minimize contact area between the holding lugs of the vane and the holding blocks, the lugs 48 in each row are spaced axially of the turbine toprovide gaps 49 between lugs, thereby reducing conductive heat transfer from the vane to the holding blocks and the blade ring.

In order to supply a uniform amount of cooling air to each vane, a cover member 54 is secured on the outer shroud portion 28, as by brazing, between the two rows of holding lugs 48 to provide a separate air chamber for each vane structure. Cooling air is admitted from the space between the blade ring 16 and the cover 20 through an opening (not shown) in the blade ring, the opening 50 in the holding block 32, an opening 56 in the cover member 54, and into the interior of the vane 26 through an opening 58 in the outer shroud 28. the air is exhausted from the vane through openings 60 in the downstream edge of the vane. The cooling air may be supplied I by a compressor (not shown) or other suitable source and admitted into the space inside the blade ring cover 20' through an opening 62 in the cover 20, see FIG. 1. Separate cooling air chambers permit separate metering of air to each chamber so that failure of any one vane will not rob its neighbors of their air supply. Also, the fit between the holding block 32 and a flange 64 around the opening 56 in the cover 54 may be made such that a gap is provided to permit compressed air to escape to cool the ambient air surrounding the outside of the cooling chamber.

- As shown more clearly in FIG. 6, the holding lugs 48 on a vane structure 12 are slid axially of the turbine in the grooves 44 and 46 in two adjacent holding blocks 32 to install the vane structure in the turbine. As shown in FIG. 1, downstream movement of the vane structure is limited by a spacing member 66 secured to the blade ring 16. When the vane structures are installed, a portion 68 on each shroud 28 overlaps a portion 70 on an adjacent shroud see FIG. 7. Upstream movement of the vane structure during operation of the turbine is prevented by the pressure of the motivating fluid. This manner of supporting the separate vane structures in the turbine permits easy removal for inspection and/or replacement of any vane structure without removal of the turbine blade ring cover.

Another advantage of the single over the multiple vane concept is in the economics of vane replacement. It is well known that in the use of high temperature ate 'als where r e life can be a overni fac t ere ls a large fiffei nce between the maxirfium and the average life of the materials resulting in a reduction of the life of one vane compared with its neighbors. When multiple vane segments are used, failure of one vane will require the replacement of the entire group. In view of these factors, the average life of a row of single vanes will greatly exceed the life of a row of multi-vane segments.

From the foregoing description, it is apparent that the invention provides a turbine stator vane structure and supporting means for the vane structure which have numerous advantages over prior structures. The structures herein disclosed are particularly suitable for use in the first stage of a multi-stage axial flow gas turbine.

We claim as our invention: 1. In an axial flow hot elastic fluid turbine, in combination,

a stator blade ring, an annular array of holding blocks attached to said blade ring, an annular array of separate stator vane structures for directing hot motive fluid, in an axial direction, said blocks being interposed between said vane structures and said blade ring, said blocks having axially extending grooves, said vane structures being slidably supported in said grooves, means for restraining movement of said vane structures in said axial direction, and means for permitting slidable disengagement of said vane structures from said blocks by movement in a direction opposite to said axial direction. 2. The combination defined in claim 1, wherein each vane structure includes holding means slidably disposed in said grooves. 3. The combination defined in claim 2, wherein the holding means comprises two transversely spaced rows of lugs, each of said rows including a plurality of mutually spaced lugs. 4. The combination defined in claim 3, wherein the lugs in each row are spaced from each other in axial direction. 5. The combination defined in claim 1, wherein the vanes are of a hollow construction, and each holding block has an opening therethrough admitting coiling air into a single vane. 6. The combination defined in claim 5, including a cover member secured to each vane structure to provide a separate cooling air chamber for each vane. 7. The combination defined in claim 3, wherein the holding lugs for each vane structure are disposed in grooves in mating two oppositely adjacent holding blocks. 

1. In an axial flow hot elastic fluid turbine, in combination, a stator blade ring, an annular array of holding blocks attached to said blade ring, an annular array of separate stator vane structures for directing hot motive fluid, in an axial direction, said blocks being interposed between said vane structures and said blade ring, said blocks having axially extending grooves, said vane structures being slidably supported in said grooves, means for restraining movement of said vane structures in said axial direction, and means for permitting slidable disengagement of said vane structures from said blocks by movement in a direction opposite to said axial direction.
 2. The combination defined in claim 1, wherein each vane structure includes holding means slidably disposed in said grooves.
 3. The combination defined in claim 2, wherein the holding means comprises two transversely spaced rows of lugs, each of said rows including a plurality of mutually spaced lugs.
 4. The combination defined in claim 3, wherein the lugs in each row are spaced from each other in axial direction.
 5. The combination defined in claim 1, wherein the vanes are of a hollow construction, and each holding block has an opening therethrough admitting colling air into a single vane.
 6. The combination defined in claim 5, including a cover member secured to each vane structure to provide a separate cooling air chamber for each vane.
 7. The combination defined in claim 3, wherein the holding lugs for each vane structure are disposed in grooves in mating two oppositely adjacent holding blocks. 